Maybe whm/war could be done moderate decent...
My only experience with whm trying something very out of the box was trying whm/war with sole sushi and swinging a capped hammer around at 36-38. It was an all LS party so they accepted allowing me to try something very unusual. Me and a smn/whm were sharing healing. So they would do DDing bloodpacts and I would be curing/regening/erasing as the needs arised. I think I did about 10-15% of the total damage while being the main healer and not slowing down xp from a lack of mp.
Since me and the smn switched off all the healing, I tried to time it so I would rest longer when berserk wasn't up. If I was 38+ the whole time I'm sure I could've put out mostly 40ish hits instead of 20-30s. At 38 whm gets access to a hammer with far more DMG than previous clubs.
I know about rdm/wars that've tanked for chain 5 parties, but I think having fast cast, phalax, and convert make it much more defense and downtime friendly.
I'm of the opinion a whm can chip in 'somewhat' with DDing when they have spare time, while properly doing their healing role in some setups. I'm specficlly thinking about VT-low incs xping, not high-inc xping. Tanking though...I have no experience trying it. I think whm/war with defense food, actually equipping defensive gear, a nice hammer and shield, flash, defender might be ok...But surely not great.
If there are jobs of the original 15(for NAs they're original anyway) that can tank well or semi-decent in xp situations besides pld,nin, and war/'insert possible sub', I believe it would be rdm/war and mnk/war with cross counters, not whm/war. Before someone wants to argue rdm/war and mnk/war, I think they'd be way more situational than the popular ninja and pld tanks. Plus people just don't like the idea of it, me and few others excluded.